WO2021131889A1

WO2021131889A1 - Non-aqueous electrolyte power storage element and method for manufacturing same

Info

Publication number: WO2021131889A1
Application number: PCT/JP2020/046699
Authority: WO
Inventors: 尽哉上田
Original assignee: 株式会社Ｇｓユアサ
Priority date: 2019-12-23
Filing date: 2020-12-15
Publication date: 2021-07-01
Also published as: DE112020006384T5; US20230033180A1; JPWO2021131889A1; CN115210904A

Abstract

One aspect of the present invention is a non-aqueous electrolyte power storage element including a negative electrode having metallic lithium, a non-aqueous electrolyte including a fluorinated solvent, and a separator having an air permeation resistance of 150 sec or less.

Description

Non-aqueous electrolyte power storage element and its manufacturing method

The present invention relates to a non-aqueous electrolyte power storage device and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries. Metallic lithium is known as a negative electrode active material having a high energy density used in a non-aqueous electrolyte power storage element (see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2016-100065 Japanese Unexamined Patent Publication No. 07-24599

In a non-aqueous electrolyte power storage element in which metallic lithium is used as the negative electrode active material, metallic lithium may be deposited in a dendritic shape on the surface of the negative electrode during charging (hereinafter, metallic lithium in a dendritic form is referred to as “dendrite”. ".). When this dendrite grows and penetrates the separator and comes into contact with the positive electrode, it causes a short circuit. Therefore, the non-aqueous electrolyte power storage element having metallic lithium as the negative electrode active material has an inconvenience that a short circuit is likely to occur due to repeated charging and discharging.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte power storage element in which the occurrence of a short circuit is suppressed, and a method for manufacturing such a non-aqueous electrolyte power storage element. That is.

One aspect of the present invention is a non-aqueous electrolyte power storage device including a negative electrode having metallic lithium, a non-aqueous electrolyte containing a fluorinated solvent, and a separator having an air permeation resistance of 150 seconds or less.

Another aspect of the present invention comprises preparing a negative electrode having metallic lithium, preparing a non-aqueous electrolyte containing a fluorinated solvent, and preparing a separator having an air permeation resistance of 150 seconds or less. This is a method for manufacturing a non-aqueous electrolyte power storage element.

According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte power storage element in which the occurrence of a short circuit is suppressed, and a method for manufacturing such a non-aqueous electrolyte power storage element.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte power storage element according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to an embodiment of the present invention.

First, the outline of the non-aqueous electrolyte power storage element and the method for manufacturing the non-water electrolyte power storage element disclosed by the present specification will be described.

The non-aqueous electrolyte storage element according to one aspect of the present invention is a non-aqueous electrolyte storage element including a negative electrode having metallic lithium, a non-aqueous electrolyte containing a fluorinated solvent, and a separator having an air permeation resistance of 150 seconds or less. ..

The non-aqueous electrolyte power storage element is suppressed from causing a short circuit. The reason for this is not clear, but the following reasons can be inferred. By using a separator having a low air permeation resistance, the concentration distribution of lithium ions in the non-aqueous electrolyte near the surface of the negative electrode is made uniform, so that the precipitation and growth of dendrites are suppressed. Further, the deposition and growth of dendrites are suppressed by the film formed on the surface of the negative electrode by the non-aqueous electrolyte containing a fluorinated solvent. Therefore, it is presumed that the growth of dendrites is suppressed and the occurrence of short circuits is suppressed by using a non-aqueous electrolyte containing a fluorinated solvent and a separator having an air permeation resistance of 150 seconds or less. Further, according to the non-aqueous electrolyte power storage element, the occurrence of a short circuit is suppressed, so that the capacity retention rate in the charge / discharge cycle is also high.

Here, the "air permeation resistance" is a value measured by the "Garley testing machine method" based on JIS-P8117 (2009). The size of the test piece of the separator used for the measurement is 50 mm × 50 mm.
The air permeation resistance of the separator included in the non-aqueous electrolyte storage element is measured using a separator obtained from the non-aqueous electrolyte storage element disassembled by the following method. First, after discharging the non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element is disassembled in a dry atmosphere. Next, the separator is taken out, washed with hydrochloric acid having a concentration of 36% by mass, further washed with deionized water, and then vacuum dried at room temperature for 10 hours or more. Then, the vacuum-dried separator is cut out and used as a test piece.

The negative electrode provided in the non-aqueous electrolyte power storage element may or may not have metallic lithium at least in the charged state, and may or may not have metallic lithium in the discharged state. For example, in the charged state, metallic lithium is deposited in at least a part of the negative electrode surface, and by discharging, substantially all of the metallic lithium on the negative electrode surface is eluted into the non-aqueous electrolyte, and in the discharged state, it is discharged. It may be a non-aqueous electrolyte power storage element configured so that metallic lithium is substantially eliminated from the surface of the negative electrode.

It is preferable that the air permeation resistance is 50 seconds or more and 80 seconds or less. By using such a separator having an air permeation resistance, the occurrence of a short circuit in the non-aqueous electrolyte power storage element is further suppressed.

It is preferable that the separator has a base resin and inorganic particles dispersed in the base resin. By using such a separator, the occurrence of a short circuit in the non-aqueous electrolyte power storage element is further suppressed. The reason why such an effect occurs is not clear, but the state in which the separator has a suitable porous shape due to the presence of the inorganic particles and the strength of the separator is increased due to the presence of the inorganic particles, and the separator is pressurized. Even if it is, it is presumed that a suitable porous shape can be maintained and good high permeability is maintained.

The positive electrode potential at the end-of-charge voltage during normal use of the non-aqueous electrolyte power storage element is 4.30 V vs. It is preferably Li / Li ^{+ or more.} By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, the discharge capacity can be increased and the energy density can be increased. In addition, the positive electrode potential is 4.30 V vs. When charging and discharging to a high potential of Li / Li ⁺ or higher are repeated, the amount of electricity used to decompose the components with low oxidation resistance in the non-aqueous electrolyte at the positive electrode causes the precipitation and growth of dendrites at the negative electrode. It is thought that short circuits are likely to occur due to use. Therefore, the advantages of the present invention that eliminate such inconvenience can be fully enjoyed.

The method for producing a non-aqueous electrolyte power storage element according to one aspect of the present invention is to prepare a combination of a positive electrode and a negative electrode having metallic lithium or a negative electrode having a surface region where metallic lithium can be deposited during charging, and a fluorination solvent. It is a method for manufacturing a non-aqueous electrolyte power storage element, which comprises preparing a non-aqueous electrolyte containing the above-mentioned material and preparing a separator having an air permeation resistance of 150 seconds or less.

According to the manufacturing method, it is possible to manufacture a non-aqueous electrolyte power storage element in which the occurrence of a short circuit is suppressed.

Hereinafter, a method for manufacturing a non-aqueous electrolyte power storage element and a non-aqueous electrolyte power storage element according to an embodiment of the present invention will be described in order.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, as an example of the non-aqueous electrolyte power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the container, a known metal container, resin container or the like which is usually used as a container for a secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer arranged directly on the positive electrode base material or via an intermediate layer.

The positive electrode base material has conductivity. The A has a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, "non-conductive", means that the volume resistivity is 10 ⁷ Ω · cm greater. As the material of the positive electrode base material, metals such as aluminum, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, as a form of forming the positive electrode base material, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

The average thickness of the positive electrode base material is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material. The "average thickness" means a value obtained by dividing the punching mass when punching a base material having a predetermined area by the true density of the base material and the punching area. The same applies to the "average thickness" of the negative electrode base material and the negative electrode active material layer, which will be described later.

The intermediate layer is a coating layer on the surface of the positive electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the positive electrode base material and the positive electrode active material layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles.

The positive electrode active material layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture forming the positive electrode active material layer may contain an optional component such as a conductive agent, a binder, a thickener, and a filler, if necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the positive electrode active material include _{a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanion compound, a chalcogen compound, sulfur and the like. Examples of the lithium transition metal composite oxide having an _{α-NaFeO type 2} _{crystal structure include Li [Li x} Ni _1-x ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co _{1-x. -Γ} ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Co _1-x ] O ₂ (0 ≦ x <0.5),
Li [Li _x Ni _γ Mn _1-x-γ ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Ni _γ Mn _β Co _1-x-γ-β ] O ₂ (0 ≦ x <0.5, 0 <γ, 0 <β, 0.5 <γ + β <1), Li [Li _x Ni _γ Co _β Al _1-x-γ-β ] O ₂ (0 ≦ x < Examples thereof include 0.5, 0 <γ, 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _2-γ O ₄ . Examples of the polyanion compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of these materials may be mixed and used.

The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. Here, the "average particle size" is based on JIS-Z-8825 (2013), and is based on the particle size distribution measured by a laser diffraction / scattering method with respect to a diluted solution obtained by diluting the particles with a solvent. It means a value at which the volume-based integrated distribution calculated in accordance with Z-8891-2 (2001) is 50%.

A crusher, a classifier, etc. are used to obtain particles of the positive electrode active material in a predetermined shape. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow type jet mill, a sieve, and the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry and wet types.

The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 98% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and further preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material in the above range, the electric capacity of the secondary battery can be increased.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials; metals; conductive ceramics and the like. Examples of carbonaceous materials include graphite and carbon black. Examples of the type of carbon black include furnace black, acetylene black, and ketjen black. Among these, a carbonaceous material is preferable from the viewpoint of conductivity and coatability. Of these, acetylene black and ketjen black are preferable. Examples of the shape of the conductive agent include powder, sheet, and fibrous.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 40% by mass or less, and more preferably 2% by mass or more and 10% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the secondary battery can be increased.

Examples of the binder include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, and styrene butadiene. Elastomers such as rubber (SBR) and fluororubber; polysaccharide polymers and the like can be mentioned.

The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 6% by mass or less. By setting the content of the binder in the above range, the active material can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate the functional group by methylation or the like in advance. In one aspect of the present invention, it may be preferable that the thickener is not contained in the positive electrode active material layer.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and water. Hydroxides such as aluminum oxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite, zeolite , Apatite, kaolin, mulite, spinel, olivine, sericite, bentonite, mica and other mineral resource-derived substances, or man-made products thereof. In one aspect of the present invention, it may be preferable that the filler is not contained in the positive electrode active material layer.

The positive electrode active material layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners and fillers. It may be contained as a component other than.

(Negative electrode)
The negative electrode has a negative electrode base material and a negative electrode active material layer arranged directly on the negative electrode base material or via an intermediate layer. The intermediate layer of the negative electrode can have the same structure as the intermediate layer of the positive electrode.

The negative electrode base material may have the same structure as the positive electrode base material, but as the material, metals such as copper, nickel, stainless steel, nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. .. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode base material is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the negative electrode base material.

The negative electrode active material layer has metallic lithium. Metallic lithium is a component that functions as a negative electrode active material. The metallic lithium may exist as pure metallic lithium consisting substantially only of lithium, or may exist as a lithium alloy containing other metallic components. Examples of the lithium alloy include a lithium silver alloy, a lithium zinc alloy, a lithium calcium alloy, a lithium aluminum alloy, a lithium magnesium alloy, a lithium indium alloy and the like. The lithium alloy may contain a plurality of metal elements other than lithium.

The negative electrode active material layer may be a layer substantially composed of metallic lithium only. The lithium content in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass.

The negative electrode active material layer may be a lithium foil or a lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). Further, the negative electrode active material layer may be a porous layer having particles containing metallic lithium. The negative electrode active material layer, which is a porous layer having particles containing metallic lithium, may further have, for example, resin particles, inorganic particles, and the like. The average thickness of the negative electrode active material layer is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and further preferably 30 μm or more and 300 μm or less.

In the charged state, metallic lithium is deposited on at least a part of the negative electrode surface, and the non-aqueous electrolyte is configured so that substantially all of the metallic lithium on the negative electrode surface is eluted into the non-aqueous electrolyte by discharging. In the case of the power storage element, the negative electrode does not have to have the negative electrode active material layer in the discharged state.

(Separator)
The separator is not particularly limited as long as it has an air permeation resistance of 150 seconds or less, and can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one surface or both surfaces of the base material layer can be used. From the viewpoint of further suppressing the occurrence of short circuits, a separator composed of only the base material layer may be preferable.

Examples of the form of the base material layer of the separator include a woven fabric, a non-woven fabric, a porous resin film, and the like, and a porous resin film is preferable. The material of the base material layer of the separator is usually a resin. As the resin (base resin) used as the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are composited may be used.

The separator preferably has a base resin and inorganic particles dispersed in the base resin. By using a separator in which the inorganic particles are dispersed in the base resin, the occurrence of a short circuit in the non-aqueous electrolyte power storage element is further suppressed. In a separator having a base resin and inorganic particles dispersed in the base resin, a base layer is usually formed by the base resin and the inorganic particles. At this time, the separator is more preferably a separator composed only of the base material layer, that is, a separator having no other layer such as a heat-resistant layer. Since the inorganic particles are dispersed and contained in the base material layer of the separator, the separator can have good heat resistance even when there is no heat-resistant layer. The base material layer may further contain components other than the base material resin and the inorganic particles.

Specific types of the base resin include the above-mentioned resin as the material of the base layer of the separator.

Specific types of materials constituting the inorganic particles include oxidation of iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, aluminosilicate and the like. Substances; hydroxides such as magnesium hydroxide, calcium hydroxide, aluminum hydroxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; calcium fluoride, barium fluoride Poorly soluble ion crystals such as silicon, covalent crystals such as diamond; talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mulite, spinel, olivine, cericite, bentonite, mica and other mineral resource-derived substances or these Artificial products, etc. As the inorganic compound, a simple substance or a complex of these substances may be used alone, or two or more kinds thereof may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the non-aqueous electrolyte power storage element.

The content of the inorganic particles in the base material layer is preferably 1% by mass or more and 70% by mass or less, more preferably 5% by mass or more and 50% by mass or less, and further preferably 10% by mass or more and 20% by mass or less. When the content of the inorganic particles is in the above range, the occurrence of a short circuit in the non-aqueous electrolyte power storage element is further suppressed. Further, when the content of the inorganic particles is within the above range, the balance between the strength (pressure resistance in the thickness direction), the flexibility, the resistance to tearing, and the like is optimized.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass loss of 5% or less when heated from room temperature to 500 ° C. in the atmosphere, and a mass loss of 5% when heated from room temperature to 800 ° C. in the atmosphere. The following are more preferable. Inorganic compounds can be mentioned as materials whose mass loss when heated is less than or equal to a predetermined value. Examples of the inorganic compound include those described above as materials constituting the inorganic particles in the base material layer. Among the inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the non-aqueous electrolyte power storage element.

The air permeation resistance of the separator is preferably 30 seconds or more and 150 seconds or less, more preferably 35 seconds or more and 100 seconds or less, and further preferably 50 seconds or more and 80 seconds or less. By using a separator having an air permeation resistance in the above range, the occurrence of a short circuit in the non-aqueous electrolyte power storage element is further suppressed. The air permeability resistance of the separator is adjusted by the porosity of the separator, the average thickness, and the like. Further, as a separator having such an air permeation resistance, a commercially available product can be used.

The average thickness of the separator is, for example, preferably 3 μm or more and 50 μm or less, and more preferably 10 μm or more and 25 μm or less. When the average thickness of the separator is at least the above lower limit, the occurrence of a short circuit can be further suppressed. On the other hand, when the average thickness of the separator is not more than the above upper limit, it is possible to increase the energy density of the non-aqueous electrolyte power storage element. The average thickness of the separator shall be the average value of the thickness measured at any 10 locations.

(Non-aqueous electrolyte)
The non-aqueous electrolyte contains a fluorinated solvent. The non-aqueous electrolyte may be a non-aqueous electrolyte solution containing a non-aqueous solvent containing a fluorination solvent and an electrolyte salt dissolved in the non-aqueous solvent.

The fluorinated solvent is a solvent having a fluorine atom. The fluorinated solvent may be one in which some or all of the hydrogen atoms in the hydrocarbon group in the non-aqueous solvent having a hydrocarbon group are replaced with fluorine atoms. Since the non-aqueous electrolyte contains a fluorinated solvent, the occurrence of a short circuit is suppressed. Further, by using the fluorinated solvent, the oxidation resistance is enhanced, and good charge / discharge cycle performance can be maintained even in charging when the positive electrode potential during normal use reaches a high potential. Examples of the fluorinated solvent include fluorinated carbonate, fluorinated carboxylic acid ester, fluorinated phosphoric acid ester, fluorinated ether and the like. As the fluorination solvent, one kind or two or more kinds can be used.

Among the fluorinated solvents, fluorinated carbonate is preferable, and it is more preferable to use fluorinated cyclic carbonate and fluorinated chain carbonate in combination. By using the fluorinated cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte can be improved. By using the fluorinated chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When the fluorinated cyclic carbonate and the fluorinated chain carbonate are used in combination, the volume ratio of the fluorinated cyclic carbonate and the fluorinated chain carbonate (fluorinated cyclic carbonate: fluorinated chain carbonate) is, for example, 5:95. It is preferably in the range of 50:50.

As the lower limit of the content ratio of fluorinated carbonate in the fluorinated solvent, 50% by volume is preferable, 70% by volume is more preferable, and 90% by volume is further preferable. The upper limit of the content ratio of fluorinated carbonate in the fluorinated solvent may be 100% by volume.

Examples of the fluorinated cyclic carbonate include fluorinated ethylene carbonate such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonate, and fluorinated butylene carbonate. Among these, fluorinated ethylene carbonate is preferable, and FEC is more preferable. FEC has high oxidation resistance and is highly effective in suppressing side reactions (oxidative decomposition of non-aqueous solvents, etc.) that may occur during charging and discharging of secondary batteries.

Examples of the fluorinated chain carbonate include trifluoromethylethyl carbonate, trifluoroethylmethyl carbonate, bis (trifluoromethyl) carbonate, and bis (trifluoroethyl) carbonate.

Examples of the fluorinated carboxylic acid ester include

methyl

3,3,3-trifluoropropionate, acetic acid-2,2,2-trifluoroethyl and the like.

Examples of the fluorinated phosphate ester include tris phosphate (2,2-difluoroethyl) and tris phosphate (2,2,2-trifluoroethyl).

Examples of the fluorinated ether include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methylheptafluoropropyl ether, methyl nonafluorobutyl ether and the like.

The non-aqueous solvent may contain a non-aqueous solvent other than the fluorinated solvent. Examples of such a non-aqueous solvent include carbonates, carboxylic acid esters, phosphoric acid esters, ethers and the like other than the fluorination solvent.

As the lower limit of the content ratio of the fluorinated solvent to the total non-aqueous solvent, 50% by volume is preferable, 70% by volume is more preferable, and 90% by volume is further preferable. By increasing the content ratio of the fluorinated solvent in the non-aqueous solvent, it is possible to further improve the short-circuit inhibitory property, oxidation resistance, and the like.

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like. Of these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such _{as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ _{, LiSO 3} CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO _2). C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other halogenated hydrocarbon groups Examples thereof include lithium salts having. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable.

The content of the electrolyte salt in the nonaqueous electrolyte is preferable to be 0.1 mol / dm ³ or more 2.5 mol / dm ³ or less, more preferable to be 0.3 mol / dm ³ or more 2.0 mol / dm ³ or less, more preferable to be 0.5 mol / dm ³ or more 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives. Examples of the additive include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, and a partially hydride of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2-fluorobiphenyl, o. -Partial halides of the above aromatic compounds such as cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and the like. Anisole halide compounds; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfite, ethylene sulfate, Sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4'-bis (2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl- Examples thereof include 2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetraxtrimethylsilyl titanate and the like. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, and 0.2. It is more preferably mass% or more and 5 mass% or less, and particularly preferably 0.3 mass% or more and 3 mass% or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or charge / discharge cycle performance after high-temperature storage, and further improve the safety.

In the secondary battery (non-aqueous electrolyte power storage element), the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V vs. It is preferably Li / Li ⁺ or higher, 4.35 V vs. It is more preferably Li / Li ⁺ or more, 4.40 V vs. In some cases, it is more preferably Li / Li ^{+ or higher.} By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, the discharge capacity can be increased and the energy density can be increased.

Note that "during normal use" refers to the case where the non-aqueous electrolyte storage element is used by adopting the charging conditions recommended or specified for the non-aqueous electrolyte storage element. For example, when a charger for the non-aqueous electrolyte power storage element is prepared, it means a case where the charger is applied to use the non-aqueous electrolyte power storage element.

The upper limit of the positive electrode potential at the end-of-charge voltage during normal use of the secondary battery is, for example, 5.0 V vs. Li / Li ⁺ , 4.8V vs. It may be Li / Li ⁺ , 4.7 V vs. It may be Li / Li ^+.

In the non-aqueous electrolyte power storage element, it is preferable that at least a part of the electrode body composed of the positive electrode, the negative electrode and the separator is in a pressurized state. Due to such pressurization, the capacity retention rate in repeated charging and discharging tends to increase. For example, the electrode body housed in the container may be pressurized from the outside of the container, that is, through the container. The electrode body is preferably pressurized in the direction in which the positive electrode, the negative electrode and the separator are overlapped (the thickness direction of each layer). That is, it is preferable that the positive electrode active material layer and the negative electrode active material layer are pressurized in the direction of being crushed in the thickness direction. However, a part of the electrode body (for example, a pair of curved surfaces in a flat winding type electrode body) may not be pressurized. Further, only a part of the flat portion of the laminated electrode body and the flat wound electrode body may be pressurized. The pressure applied to at least a part of the electrode body in the pressurized state or the pressure applied to the container from the outside is preferably 0.01 MPa or more and 2 MPa or less, more preferably 0.1 MPa or more and 1.5 MPa or less, and 0.2 MPa. More preferably 1 MPa or less. By setting the pressure to be equal to or higher than the lower limit, the capacity retention rate can be increased more sufficiently. On the other hand, by setting the pressure to be equal to or lower than the upper limit, the occurrence of a short circuit due to repeated charging and discharging is further suppressed.

The pressurization of the electrode body can be performed by, for example, a pressurizing member that pressurizes the container from the outside. The pressurizing member may be a restraining member that restrains the shape of the container. The pressurizing member (restraint member) is provided so as to pressurize the electrode body by sandwiching it from both sides in the thickness direction via, for example, a container. The pressurized surface of the electrode body is in contact with the inner surface of the container, either directly or via another member. Therefore, when the container is pressurized, the electrode body is pressurized. Examples of the pressurizing member include a restraint band and a metal frame. For example, in a metal frame, the load may be adjustable by bolts or the like. Further, a plurality of non-aqueous electrolyte storage elements are arranged side by side in the thickness direction of the electrode body, and the plurality of non-aqueous electrolyte storage elements are pressed from both ends in the thickness direction and fixed by using a frame or the like. May be good.

Dendrite tends to grow when the current density during charging is high. Therefore, the non-aqueous electrolyte power storage device according to the embodiment of the present invention can be suitably applied to applications in which charging with a high current density is performed. Examples of such applications include power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid vehicles (PHEVs), power supplies for flying objects such as airplanes and drones, and power supplies for regenerative power charging. Be done. Above all, the non-aqueous electrolyte power storage element is particularly suitable for an air vehicle power supply because it has an extremely high mass energy density particularly required for an air vehicle power supply and a sufficient charge / discharge cycle performance.

The shape of the non-aqueous electrolyte power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.

FIG. 1 shows a non-aqueous electrolyte power storage element 1 as an example of a square battery. The figure is a perspective view of the inside of the container. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

<Configuration of non-aqueous electrolyte power storage device>
The non-aqueous electrolyte power storage element of the present embodiment includes a power source for automobiles such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid vehicle (PHEV), a power source for an airplane, a vehicle such as a drone, a personal computer, and communication. It can be mounted as a power storage unit (battery module) composed of a plurality of non-aqueous electrolyte power storage elements assembled on a power supply for electronic devices such as terminals, a power supply for power storage, or the like. In this case, the technique according to the embodiment of the present invention may be applied to at least one non-aqueous electrolyte power storage element included in the power storage unit.

FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 1 are assembled is further assembled. The power storage device 30 includes a bus bar (not shown) that electrically connects two or more non-aqueous electrolyte power storage elements 1, a bus bar (not shown) that electrically connects two or more power storage units 20 and the like. May be good. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte power storage elements.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing a non-aqueous electrolyte power storage element according to an embodiment of the present invention is to prepare a combination of a positive electrode and a negative electrode having metallic lithium or a negative electrode having a surface region where metallic lithium can be deposited during charging, and fluorination. A non-aqueous electrolyte containing a solvent is prepared, and a separator having an air permeation resistance of 150 seconds or less is prepared.

Preparing a negative electrode having metallic lithium may be producing a negative electrode having metallic lithium. The negative electrode can be manufactured by laminating a negative electrode active material layer containing metallic lithium directly on the negative electrode substrate or via an intermediate layer and pressing the negative electrode. The negative electrode active material layer containing metallic lithium may be a lithium foil or a lithium alloy foil. As a specific form and a preferable form of the prepared negative electrode, the above-mentioned form can be applied as the negative electrode provided in the non-aqueous electrolyte power storage element.

The negative electrode having a surface region on which metallic lithium can be deposited during charging may be, for example, a negative electrode composed of only a negative electrode base material. When preparing a negative electrode having a surface region on which metallic lithium can be deposited during charging, a positive electrode having a positive electrode active material containing lithium ions is prepared in advance as the positive electrode.

Preparing a non-aqueous electrolyte containing a fluorinated solvent may be preparing a non-aqueous electrolyte containing a fluorinated solvent. The non-aqueous electrolyte can be prepared by mixing each component constituting the non-aqueous electrolyte, such as a fluorinated solvent and other components. As a specific form and a preferred form of the non-aqueous electrolyte to be prepared, the above-mentioned form can be applied as the non-aqueous electrolyte provided in the non-aqueous electrolyte power storage element.

Preparing a separator having an air permeation resistance of 150 seconds or less may be the preparation or purchase of a commercially available product of such a separator, or the production of such a separator. As a specific form and a preferable form of the prepared separator, the above-mentioned form can be applied as a separator provided in the non-aqueous electrolyte power storage element.

For example, the method for manufacturing the non-aqueous electrolyte power storage element includes preparing or manufacturing a positive electrode, preparing or manufacturing a negative electrode, preparing or preparing a non-aqueous electrolyte, preparing or manufacturing a separator, a positive electrode and a negative electrode. To form an electrode body that is alternately superimposed by laminating or winding through a separator, to house the positive electrode and the negative electrode (electrode body) in a container, and to inject the non-aqueous electrolyte into the container. To be equipped with. After the injection, the non-aqueous electrolyte power storage element can be obtained by sealing the injection port.

<Other Embodiments>
The present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (for example, a lithium ion secondary battery) has been described. The capacity and the like are arbitrary. The non-aqueous electrolyte power storage element of the present invention can also be applied to capacitors such as various non-aqueous electrolyte secondary batteries, electric double layer capacitors and lithium ion capacitors.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

The separators used in Examples and Comparative Examples are shown below. As the base resin, those produced by biaxial stretching were used.
Separator A: A separator (without a heat-resistant layer) composed of a base material layer having an air permeation resistance of 35 seconds, an average thickness of 16 μm, and inorganic particles dispersed in a base material resin (polyolefin resin), in the base material layer. Content of inorganic particles 50% by mass
Separator B: A separator (without a heat-resistant layer) composed of a base material layer having an air permeation resistance of 45 seconds, an average thickness of 16 μm, and inorganic particles dispersed in a base material resin (polyolefin resin), in the base material layer. Content of inorganic particles 25% by mass
Separator C: A separator (without a heat-resistant layer) composed of a base material layer having an air permeation resistance of 70 seconds, an average thickness of 16 μm, and inorganic particles dispersed in a base material resin (polyolefin resin), in the base material layer. Content of inorganic particles 15% by mass
Separator D: Air permeability resistance 90 seconds, average thickness 21 μm, separator consisting of a base material layer consisting only of a base resin (polyolefin resin) and a heat-resistant layer Separator E: Air permeability resistance 172 seconds, average thickness 17 μm, separator / separator F consisting of a base material layer consisting only of a base resin (polyolefin resin) and a heat-resistant layer: air permeability resistance 286 seconds, average thickness 25 μm, from only a base resin (polyolefin resin) Separator / Separator G made of a base material layer: A separator made of a base material layer and a heat-resistant layer having an air permeability resistance of 300 seconds, an average thickness of 24 μm, and a base material resin (polyolefin resin) only.

[Example 1]
(Preparation of positive electrode)
As the positive electrode active material, _{a lithium transition metal composite oxide having an α-NaFeO type 2} crystal structure and represented by Li _{1 + α} Me _1-α O ₂ (Me is a transition metal) was used. Here, the molar ratio of Li and Me, Li / Me, was 1.33, and Me was composed of Ni and Mn and contained in a molar ratio of Ni: Mn = 1: 2.

Using N-methylpyrrolidone (NMP) as a dispersion medium, the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder have a mass ratio of 94: 4.5: 1.5. A positive electrode paste contained in the above was prepared. The positive electrode paste was applied to one side of an aluminum foil having an average thickness of 15 μm, which is a positive electrode base material, dried, pressed, and cut, and a positive electrode active material layer was arranged in a rectangular shape having a width of 30 mm and a length of 40 mm. A positive electrode was prepared.

(Preparation of negative electrode)
A lithium foil (100% by mass of metallic lithium) having an average thickness of 100 μm is laminated as a negative electrode active material layer on one side of a copper foil having an average thickness of 10 μm, which is a negative electrode base material. A negative electrode was produced by cutting into a shape.

(Preparation of non-aqueous electrolyte)
_{LiPF 6} was dissolved in a mixed solvent in which fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) were mixed at a volume ratio of 30:70 at a concentration of 1 mol / dm ³ , and a non-aqueous electrolyte was prepared. And said.

(Manufacturing of non-aqueous electrolyte power storage element)
An electrode body was produced by laminating the positive electrode and the negative electrode via the separator A. The non-aqueous electrolyte power storage element (secondary battery) of Example 1 in which the electrode body is housed in a container, the above-mentioned non-aqueous electrolyte is injected into the container, the container is sealed, and the container is pressurized at 0.3 MPa from the outside. ) Was obtained.

[Examples 2 to 4 and Comparative Examples 1 to 5]
Non-aqueous electrolyte power storage devices of Examples 2 to 4 and Comparative Examples 1 to 5 in the same manner as in Example 1 except that the type of separator and the composition of the non-aqueous solvent of the non-aqueous electrolyte are as shown in Table 1. Got In the table, EC represents ethylene carbonate and EMC represents ethyl methyl carbonate.

(Initial charge / discharge)
Each of the obtained non-aqueous electrolyte power storage elements was initially charged and discharged under the following conditions. At 25 ° C., constant current and constant voltage charging was performed with a charging charge of 0.1 C and a charge termination voltage of 4.60 V. The charging end condition was until the charging current reached 0.02C. Then, a 10-minute rest period was provided. Then, a constant current discharge was performed with a discharge current of 0.1 C and a discharge end voltage of 2.00 V, and then a rest period of 10 minutes was provided. This charge / discharge cycle was performed for two cycles.

(Charge / discharge cycle test)
Then, the following charge / discharge cycle test was performed. At 25 ° C., constant current and constant voltage charging was performed with a charging current of 1C and a charging termination voltage of 4.60V. The charging end condition was until the charging current reached 0.05C. Then, a 10-minute rest period was provided. After that, constant current discharge was performed with a discharge current of 1C and a discharge end voltage of 2.00V, and then a rest period of 10 minutes was provided. This charge / discharge cycle was repeated, and the number of cycles until a short circuit occurred was recorded. The discharge capacity retention rate was determined for those in which the number of cycles until a short circuit occurred exceeded 25 times. The discharge capacity retention rate was set to the discharge capacity of the 25th cycle with respect to the discharge capacity of the 5th cycle. The results are shown in Table 1.

As shown in Table 1, Comparative Examples 1 and 5 using a non-aqueous electrolyte containing no fluorinated solvent, and Comparative Examples 2 to 5 using a separator having an air permeation resistance of more than 150 seconds are 20. A short circuit occurred with a small number of cycles less than the number of cycles. On the other hand, in the non-aqueous electrolyte power storage elements of Examples 1 to 4 using the non-aqueous electrolyte containing the fluorinated solvent and the separator having an air permeation resistance of 150 seconds or less, the number of cycles until a short circuit occurs is 40. The number of times was exceeded, the occurrence of short circuits was sufficiently suppressed, and the discharge capacity retention rate was also high. Above all, in the non-aqueous electrolyte power storage element of Example 3, the occurrence of a short circuit was particularly suppressed, probably because the air permeability resistance of the separator was particularly appropriate.

The present invention can be applied to electronic devices such as personal computers and communication terminals, non-aqueous electrolyte power storage elements used as power sources for automobiles, and the like.

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims

Negative electrode with metallic lithium,
A non-aqueous electrolyte power storage device including a non-aqueous electrolyte containing a fluorinated solvent and a separator having an air permeation resistance of 150 seconds or less.
The non-aqueous electrolyte power storage element according to claim 1, wherein the air permeation resistance is 50 seconds or more and 80 seconds or less.
The non-aqueous electrolyte power storage element according to claim 1 or 2, wherein the separator has a base resin and inorganic particles dispersed in the base resin.
The non-aqueous electrolyte power storage element according to any one of claims 1 to 3, wherein the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V (vs. Li / Li +) or more.
To prepare a combination of a positive electrode and a negative electrode having metallic lithium or a negative electrode having a surface region where metallic lithium can be deposited during charging.
A method for producing a non-aqueous electrolyte power storage device, comprising preparing a non-aqueous electrolyte containing a fluorinated solvent and preparing a separator having an air permeation resistance of 150 seconds or less.